* {
  padding: 0;
  margin: 0;
}

:root {
  background: #333;
  display: flex;
  justify-content: center;
  height: 100vh;
}

#app {
  width: 500px;
  border: solid 3px greenyellow;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
}
#app img {
  width: 100%;
  aspect-ratio: 16/9;
  -o-object-fit: cover;
     object-fit: cover;
}